By Alan Buis,
NASA’s Jet Propulsion Laboratory
The twin magnitude 6.4 and 7.1 earthquakes that struck the Ridgecrest area in California’s Mojave Desert northeast of Los Angeles on July 4 and 5, respectively, were felt by up to 30 million people in California, Nevada, Arizona and Baja California, resulting in loss of life, injuries, billions in damage and lots of frazzled nerves. While the remote location undoubtedly minimized impacts, theq did serve as a wake-up call for complacent Californians that they live in Earthquake Country and need to prepare for the inevitable “Big One” that scientists say is sure to come. They also got people talking about all aspects of earthquakes.
There are lots of myths about earthquakes. A common one is that there’s such a thing as “earthquake weather” — certain types of weather conditions that typically precede earthquakes, such as hot and dry, or dry and cloudy. The myth stems from the Greek philosopher Aristotle, who proposed in the 4th century B.C. that earthquakes were caused by trapped winds escaping from subterranean caves. He believed the large amounts of air trapped underground would make weather on Earth’s surface before a quake hot and calm.
With the advent of seismology — the study of earthquakes — we now know that most quakes are caused by tectonic processes — forces within the solid Earth that drive changes in the structure of Earth’s crust, primarily the rupture of underground rock masses along faults (linear zones of weakness). We also know that most earthquakes occur far beneath Earth’s surface, well beyond the influence of surface temperatures and conditions. Finally, we know the statistical distribution of earthquakes is approximately equal across all types of weather conditions. Myth busted.
In fact, according to the U.S. Geological Survey, the only correlation that’s been noted between earthquakes and weather is that large changes in atmospheric pressure caused by major storms like hurricanes have been shown to occasionally trigger what are known as “slow earthquakes,” which release energy over comparatively long periods of time and don’t result in ground shaking like traditional earthquakes do. They note that while such large low-pressure changes could potentially be a contributor to triggering a damaging earthquake, “the numbers are small and are not statistically significant.”
But what about climate? Are there any connections between climate phenomena and earthquakes? We asked geophysicist Paul Lundgren of NASA’s Jet Propulsion Laboratory in Pasadena, California, to do a scientific shakedown on the matter.
The article is culled courtesy of NASA Global Climate Change
Categories: Human interest